Adenocarcinoma of the endometrium occurs principally in postmenopausal women. Numerous studies have been published both for and against the association of abnormal estrogen metabolism with the development of this tumor. This research protocol proposes to comprehensively evaluate in vivo estrogen metabolism in postmenopausal women with endometrial cancer and in weight- and age-matched controls. The major androgenic precursors of estrogens will also be examined. The following studies will be performed in these patients: 1) The serum levels of estrone, estradiol, androstenedione and testosterone will be measured. 2) The metabolic clearance rates and production rates of the same estrogens and androgens will be quantitated. 3) The methods currently used to measure the peripheral conversion of androstenedione to estrone will be critically evaluated, and the best method for evaluating this important metabolic process will be adopted. 4) Circulation sex hormone binding globulin and free estradiol levels will be quantitated. 5) The histology and stage of the tumors will be correlated with the endocrine results. It is also proposed that the extent of direct secretion of estrogens by the adrenal glands be assessed. Finally, the role of peripheral aromatization of androstenedione will be evaluated with the use of an in vivo inhibitor of this process.